High-energy density capacitors play a critical role in numerous military and commercial pulsed power applications; however, the current state-of-the-art technology suffers from low-energy density, making them bulky and costly. Deployment of current and future pulse power devices such as radar devices, lasers, rail guns, high-power microwaves, defibrillators and pacemakers, will continue to rely on the development of high-energy density capacitors.
Current pulse power devices often use polymer film capacitors, which include biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), polystyrene (PS), polycarbonate (PC) and polyimide (PI), all of which have the advantage of high dielectric breakdown strength. However, all the mentioned polymers have low dielectric permittivity (2-3.2), which highly limits the energy density of the capacitor. For example, the current state-of-the-art active film material for capacitors is BOPP, which offers a capacitor energy density of 1.2 J/cc, but is restricted by its low dielectric permittivity, thus limiting the size and cost of these systems.
The current challenge of pulse power devices is obtaining high energy density. Theoretically, the energy density is linearly proportional to the dielectric constant and quadratically related to the breakdown strength of the capacitor. Therefore, many efforts have been devoted to enhance the material's permittivity and/or breakdown strength to improve the energy density. Currently, commercial monolithic materials are reaching a plateau in terms of energy density, due to the trade-off between the dielectric permittivity and breakdown strength of the materials. Nanocomposites combining a high breakdown strength polymer and a high dielectric permittivity ceramic filler offer significant promise for future high-energy density capacitors. While current nanocomposites improve the dielectric permittivity of the capacitor, the gains come at the expense of the breakdown strength, which limits the ultimate performance of the capacitor. Therefore, there is an increased demand to capture high dielectric permittivity from ceramic and high breakdown strength from polymer to achieve high energy density.